[Amps] Tuned power transformer

[Ian White, G3SEK]

Angel Vilaseca wrote:
>
>I am taking apart an old HV power supply made in the late '40s, 
>probably in Germany. From its size, the power transformer should be 
>rated for approximately 1 KW. It has an HV secondary winding 800-0-800 
>Volts and two 12 V for filaments. It has a vacuum rectifier.
>
>It has tuned chokes and I also found that a 10 uF cap is wired across 
>the primary winding of the power transformer.
>
>So I guess that this must be a tuned-primary power trnsformer. I never 
>saw this before. How does this work? What are the properties of a 
>tuned-primary power transformer? Does it prevent current inrush at 
>power-on like a tuned choke?
>
>Of course, I will replace the vacuum rectifier with solid-state diodes. 
>Should I leave the 10 uF cap acros ethe primary or remove it?
>

The capacitor is probably for power factor correction.

There are a number of unusual things about this power supply, so you 
should be a little bit suspicious about the transformer.

If you can, try to see if the core configuration looks normal - look 
particularly for any deliberate gaps or magnetic shunts. Measure the 
primary and secondary DC resistances to check if those appear normal 
too, as compared with similar transformers - a few tens of ohms for the 
secondary; a few ohms maximum for the primary.

If you intend to use the whole secondary with a full-wave bridge and 
capacitor input (should give about 2kV on load), test the transformer 
with an existing power supply before you build it into a new one.


-- 
73 from Ian G3SEK
http://www.ifwtech.co.uk/g3sek